iOS 根据圆心的坐标点、半径、当前手势所在的坐标点，计算出圆的运动轨迹坐标

/**
 *  根据圆心的坐标点、半径、当前手势所在的坐标点，计算出圆的运动轨迹坐标
 *  @param radius 圆心半径
 *  @param centerCircle 圆心的坐标点
 *  @param currentPoint 当前的手势所在的坐标点
 *  @return CGPoint 返回圆的坐标
 */
+(CGPoint)CirclePoint:(CGFloat)radius withCenterCircle:(CGPoint)centerCircle withCurrentPoint:(CGPoint)currentPoint;

+(CGPoint)CirclePoint:(CGFloat)radius withCenterCircle:(CGPoint)centerCircle withCurrentPoint:(CGPoint)currentPoint
{
    CGPoint cPoint;
    CGFloat x = currentPoint.x;
    CGFloat y = currentPoint.y;
    CGFloat cX ; //圆的X坐标轨迹
    CGFloat cY ; //圆的Y坐标轨迹
    CGFloat daX; // 圆心到转动按钮的距离的平方
    //CGFloat daY;
    CGFloat aX;  // 圆心到转动按钮的距离
    //CGFloat aY;
    CGFloat cosX;  // 圆心水平方向与转动按钮形成的夹角的cos值

    //圆心与触控点的距离的平方（勾股定理）
    daX =  (x - centerCircle.x)*(x - centerCircle.x) + (y - centerCircle.y)*(y - centerCircle.y);
    aX = sqrt(daX); //开根号  //圆心与触控点的距离
    cosX =  fabs(x - centerCircle.x)/aX;  //绝对值
    cX = cosX*radius ; //  x =R * cosX;  圆心到触控点在水平坐标的X的值
    cY = sqrt(radius*radius - cX*cX);

    if(x<centerCircle.x) //如果X所在的点小于圆心 在圆心的左边
    {
        cX = centerCircle.x - cX;
    }
    else
    {
        cX = centerCircle.x + cX;
    }

    if(y<centerCircle.y)
    {
        cY = centerCircle.y - cY;
    }
    else
    {
        cY = centerCircle.y + cY;
    }
    cPoint.x = cX;
    cPoint.y = cY;
    return cPoint;
}